1. Field of the Invention
The present invention relates to ink to be applied to a person's fingertip's etc. and subsequently transferred to a recording medium to provide a pattern corresponding to the person's fingerprints, palm prints, etc.
2. Description of the Prior Art
Fingerprints have been widely used for many years to positively identify people. For many years fingerprints were obtained by dispensing a viscous carbon black pigmented ink, i.e, in a gel or paste form, from a tube onto a plate or other flat surface and rolling the fingertips of the person to be fingerprinted over the plate. The fingertips were then rolled or pressed onto a suitable recording surface, made of paper, for example. This system is referred to hereinafter as "tube/roller system".
Many of the tube inks used in the tube/roller system suffer the disadvantages of: excessively staining the skin; requiring solvent or special cleaners for cleaning of tools and of the skin; separating into layers of clear oil and black paste while in the tube; drying rapidly so as to require immediate clean-up, as opposed to being reused at a later time if left on the plate and roller; having a slippery consistency, which makes coating the fingers somewhat difficult and may result in smudged images on the recording medium. There is a need for better viscous carbon pigmented ink for use in connection with the tube/roller system which overcomes the above disadvantages.
While the conventional tube/roller system is suitable for use in police stations and the like, it is not well suited for use by banking and retail establishments because of the expertise required in providing the proper thickness of ink on the plate, space requirements and required clean-up.
Various other methods have been developed to enable such establishments to record fingerprints on a document, most of which involve either black ink or inkless chemical processes. Fingerprints, as they apply to check and credit card transactions, are used as a deterrent to fraud and to assist in the prosecution process. One of the problems with "bad check" cases is the lack of solid evidence to obtain an arrest, prosecution, and conviction. However, a fingerprint placed on the fraudulent document solves this problem. Many case studies prove that check fraud losses can be reduced by a minimum of fifty percent. In the prosecution of check fraud criminals, fingerprints historically identify suspects over ninety-two percent of the time.
The environment surrounding check and credit card transactions requires the fingerprinting ink to be nonstaining on the skin so that customers are not offended and so that clean-up is unnecessary. The ink needs to be formulated so that it may be packaged in a pad that is easy to use and in a material that will provide high, fingerprint resolution. It is desirable for the ink to possess sufficient opacity and neutrality of color for reproduction on microfiche, as checks are commonly disposed of after they have been recorded on film.
Nonpigmented inks which do not leave a visible residue on the fingertips have been available for sometime. However, these nonpigmented inks generally require the use of two separate chemical compounds. One of the compounds is applied to the fingerprint area and the other compound is impregnated into the recording surface before the fingerprinting procedure or otherwise transferred to such surface after the fingerprinting procedure to form a visible reaction product delineating the ridge pattern to form a visible fingerprint.
Pigmented inks which utilize a carbon pigment to form the visible print generally stain the fingers. Such inks conventionally comprise a carbon black dispersion in which the carbon pigment (comprising about 50% or less of the dispersion) is dispersed in paraffinic mineral oil. This dispersion must be processed, for example, by ball milling the mixture for several hours, to break up existing agglomerates before the dispersion can be diluted with a suitable solvent or carrier. One carbon pigmented ink and a microporous dispensing pad therefore which deposits a small amount of ink on the fingertips to thereby substantially eliminate staining is described in U.S. Pat. No. 5,395,444 ("'444 patent") assigned to Identicator Corporation ("Identicator"), the assignee of this application. The ink described in the '444 patent employs a carbon black pigment dispersion concentration of about 22% by weight (within the range of 15% to 30%) with the carbon black particles having an average particle size of about 0.35 microns and the particle size falling within the range of 0.15 to 0.60 microns. The '444 ink, as commercially marketed by Identicator, requires, in addition to the carbon black dispersion and a napthenic oil carrier, the addition of a polymer such as an alkylated polyvinylpyrrolidone to minimize the degree to which the graphics, such as a fingerprint, can become blurred, lose contrast and resolution. The addition of a polymer usually requires extra time for the application of heat and agitation. The carbon pigment itself, due to its light scattering properties attendant to particle size, tends to create graphics which appear brownish in color. The desired color for a fingerprint is an achromatic black. Modifying the ink so that it becomes a gel or a paste for use in the conventional tube/plate roller method, requires additional polymer which typically adds both material and processing costs. Also, the commercial '444 ink contains a red pigment in the range of 5% to 10% by weight which functions as an optical enhancer to make the print more compatible with electronic scanning equipment. In addition, the surface at the ceramic dispensing pad for the '444 commercial ink has required surface treatment with silane, for example, to reduce the interfacial surface tension of the pad. This treatment ensured that a sufficient supply of ink was available on the pad surface. However, such treatment further added to the manufacturing costs of the pad.
It has been discovered that a carbon pigmented ink in which the agglomerate size of the carbon particles is made considerably smaller than the particle size of the carbon used in the prior art inks not only overcomes many of the disadvantages described above with respect to viscous tube/roller inks and nonstaining pad inks, but provides superior print contrast (i.e., between the ridges and valleys) and is considerably less expensive than the prior art inks.